1. Field of the Invention
The present invention relates to a friction stir welding method for welding by use of a rotary tool having a pin portion and a shoulder portion. In addition, the present invention relates to a welded component part obtained by the friction stir welding method.
2. Description of the Prior Art
The friction stir welding method is a method wherein a pin portion of a rotary tool made of a material harder than members to be welded is inserted between abutment surfaces of the members to be welded, and frictional heat and plastic flow are caused at the abutment surfaces by rotation and movement of the rotary tool, thereby welding the members. One example of the friction stir welding method is described in Japanese Patent Laid-open No. 11-10368 (1999). Since the members to be welded can be welded at a temperature equal to the melting point or below thereof by the friction stir welding, this technique has the effects that strain after welding is little, the surfaces of the members remain aesthetically good, and so on.
The friction stir welding method is suitable for welding members which are the same or similar in physical properties or mechanical properties. However, where the members to be welded are conspicuously different in physical properties, for example, melting point or density, or where the members to be welded are conspicuously different in mechanical properties, the friction stir welding method results in that a defective weld is liable to be generated and a sound weld is difficult to obtain.
It is an object of the present invention to provide a friction stir welding method such that even members different in physical properties or mechanical properties can be welded in good conditions by the friction stir welding technique.
The present invention resides in that friction stir welding is conducted such that members to be welded are abutted against each other, a pin portion of a rotary tool is inserted to one of the members, while the pin portion is not inserted to the other of the members but only a shoulder portion of the rotary tool is brought into contact with the other of the members.
According to the welding method of the present invention, frictional heat and plastic flow due to a friction stir action are generated on the side of the member where the pin portion of the rotary tool is inserted, the frictional head is transferred to the member on the side where the pin portion is not inserted, and diffusion of atoms is generated in the vicinity of the abutment surfaces of both the members, whereby diffusion bonding is achieved. Thus, the present invention is not a conventional simple friction stir welding but is a novel friction stir welding.
In carrying out the welding method according to the present invention, it is desirable that a coat layer of a metal capable of easily coupling with the opponent member on a metallic basis is provided on one or both of the abutment surfaces of the members to be welded. In addition, it is desirable that holes are provided in the welding surface of the member to be welded on the side where the pin portion of the rotary tool is not inserted. Further, it is desirable that an upper surface of the member to be welded on the side where the pin portion of the rotary tool is not inserted is covered with the same material as that of the other member to be welded, and the shoulder portion of the rotary tool is brought into contact with the cover portion.